1. Statement of the Technical Field
The present invention relates to a network system which operates according to the terms of a service level agreement, and more particularly to a network system which operates at different tiers according to the terms of tier-level service level agreements.
2. Description of the Related Art
In an efficient admissions control and capacity planning policy, minimal resources can be allocated automatically to satisfy the requirements of a specified service level agreement (SLA), leaving the remaining resources for later use. SLAs are agreements between service providers and their customers which specify a minimum level of service to be provided by the service provider on behalf of its customer. Typical SLAs include one or more network traffic terms which either limit the amount and type of resources that the subscribing customer can consume for a given rate, or guarantee the amount and quality of service (QoS) of resources that the provider will provide to the subscribing customer for a given rate.
For example, a subscribing consumer can agree to an SLA in which the consumer agrees to consume only a particular quantity of network bandwidth offered by the provider. Conversely, the SLA can require the provider to guarantee access to the subscribing consumer to at least a minimum amount of bandwidth. Also, the SLA can require the provider to provide a certain QoS over the provided minimum amount of bandwidth.
When considering the terms of an SLA, content hosts provision server resources for their subscribing customers, co-hosted server applications or services, according to the resource demands of the customers at their expected loads. Since outsourced hosting can be viewed as a competitive industry sector, content hosts must manage their resources efficiently. Logically, to ensure that the customers receive the promised level of service in the SLA, content hosts can be configured to survive a worst-case load. Yet, the worst-case approach can unnecessarily tax the resources of the content host, even when those resources are not required to service a given load. Hence, rather than over-provisioning resources in the content host, efficient admission control and capacity planning policies can be designed merely to limit rather than eliminate the risk of meeting the worst-case demand.
In this regard, an efficient resource management scheme can automatically allocate to each service of a subscribing customer only the minimal amount of resources required to meet the QoS levels specified in an SLA. In consequence, surplus resources can be withheld for use by the content host to meet the requirements of other subscribing customers. Thus, resource provisioning logic must adapt to changes in load as they occur, and the resource provisioning logic must respond gracefully to unanticipated demand surges or resource failures.
Business methods for establishing and managing SLA relationships between providers and subscribing customers have been implemented in content hosting environments. Specifically, those implemented business methods manage the cost/benefit analysis associated with resource allocation choices. Yet, content hosting environments no longer exist in a vacuum. Rather, as content hosting centers become overloaded with traffic, or as content hosting centers acquire new subscribing customers based upon QoS guarantees in an SLA, functions and data processing are removed from the content host to the edge of the network.
Existing content distribution network (CDN) models include edge processing of content requests at the edge of the CDN. These existing CDN models provide for takeover or overflow service for content hosts. Specifically, where in the takeover or overflow service model of the conventional CDN, the CDN handles all traffic direction and caching for content hosts. Alternatively, the CDN agrees to handle traffic only where specific peak traffic conditions in the content host arise. Yet, existing SLA models for managing resource allocation choices wholly ignore the complete relationship between CDN, content host and data consumer.